Motion detectors are commonly used in security and other applications to detect the presence or absence of motion, and to use the information thus derived to, for example, trigger alarms or turn on lights. The simplicity and inexpensiveness of such detectors has led to their ubiquity in both industrial and domestic contexts.
Although ordinary light is sometimes used, typically such motion detectors use passive infrared sensors to sense the presence of people and animals or other sources of infrared radiation. The common component shared among all such motion detectors is the area-sensor, defined as a means of converting energy coming from a particular direction into an electrical signal, as depicted in FIG. 4.
Many patents have been issued wherein multiple area-sensors are employed. In every case, however, what is claimed in the prior art are improved methods for avoiding ‘false alarms’, e.g., accidental activation due to abrupt changes in room temperature, the motion of pets, light from the headlamps of passing cars, etc. The manner in which these devices of the prior art treat signals from their respective area-sensors teaches against the present invention.
U.S. Pat. No. 4,745,284, discloses an infrared detector that includes two pyroelectric infrared ray detecting elements electrically connected with each other to generate an output signal corresponding to the difference between them. This patent, as depicted in FIG. 1, teaches the deliberate destruction of the vectorial information by developing a scalar-only resultant signal.
U.S. Pat. No. 7,183,912, discloses a passive infrared sensor with a plurality of detector elements that detects objects by comparing the frequency of the ‘sum’ of the signals to the frequency of the ‘difference’. This prior art explicitly teaches the destruction of vectorial information as shown in FIG. 2, by combining signals from multiple area-sensors into a simple ON or OFF state for an “audible or visual alarm”.
U.S. Pat. No. 6,215,399, discloses a motion detector that monitors multiple “zones”, or areas of detection, such that when multiple “zones” generate simultaneous signals it indicates that the object is “big enough” to be a person, rather than a pet. This patent, as depicted in FIG. 3, explicitly teaches the destruction of vectorial information through the use of a “suppressor” circuit shown as element 22 in the figure.
In each case, motion detectors provide only an indication of the presence or absence of a moving object. Simple motion detection does not suffice for many applications where it is desirable to ascertain not simply whether an object is in the relevant area, but where within that area the object is located. Localizing objects, as opposed to simply detecting their presence or absence, currently requires considerably more sophisticated, and therefore expensive, electronics, optics, and substantial computing power. For example, as disclosed in U.S. Pat. No. 6,088,468, objects have been localized electronically by comparing two video images or pictures, pixel by pixel, to determine the position and movement of an object, an effective but expensive solution, often requiring extensive and specialized wiring, a separate “computer” with sophisticated software, and substantial amounts of electric power. Such devices are also prohibitively expensive for everyday household or small office use.
A need therefore exists for a simple, inexpensive apparatus and method that can be used to detect not only the presence but the location of objects, and that can be easily installed and cheaply replaced, if necessary.
Localizing an object has further advantages. e.g. a typical alarm system or lighting system turns OFF after a preset interval, even though an intruder or the object of interest remains in the area. The present invention remedies this shortcoming as the object, having been localized, is ‘known’ to remain within the detection area, even though it has stopped moving.